ИСТИНА

Measurements of energetic particle fluxes in the Earth magnetosphere at large distances from the Earth (10 Re and more) are still sparse, and registering instruments usually have high background, that does not permit to determine low particle fluxes accurately, in particular those of subrelativistic electrons. Information on these fluxes and their dynamics are very important for understanding the structure of the magnetosphere, direction of particle drifts, mechanisms of the penetration of solar particles into the magnetosphere and other details of particle-field interaction. The orbit and instrumentation of the Earth satellite IMP-8 allows to fill up this gap to some extent. IMP-8 had a nearly circular orbit with a radius of about 35 Re. The orbital period was 12 days, of which 4 days was spent in the magnetospheric tail. The fluxes of 0.2-10 MeV electrons between 1974 and 2001 are analyzed in different parts of the IMP-8 orbit: at the entrance-exit from the magnetosphere, outside of the magnetosphere and in the near- magnetospheric space. It is shown that during quite periods of solar activity, even during solar minima, electron flux enhancements in the magnetospheric tail were observed due to acceleration mechanisms in the magnetosphere, penetration of solar particles and electrons from the Jovian magnetosphere.